In general, downlights are constructed such that a light source is embedded in a ceiling hole. Such downlights have been widely used as architectural illumination means that integrate illumination with a building.
The downlight is embedded in the ceiling so as to be substantially prevented from being exposed outward, thus advantageously providing an orderly external appearance to the ceiling. Moreover, the downlight embedded in the ceiling may have low luminance and be suitable to form an intimate indoor space.
However, such an illumination unit configuration may be suitable for a narrow indoor space than a wide indoor space, and may need a great number of light sources such as Light Emitting Diodes (LEDs).
Accordingly, in the future, development of an illumination unit suitable for a wide indoor space even with a low number of LEDs is necessary.